Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.1 (S1 nuclease)
 3,660 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription of mouse mammary tumor virus DNA is stimulated by steroid hormones. The DNA sequences involved in this regulation are located in the viral long terminal repeat between positions -200 and -50 with respect to the transcription initiation site. In this region four, one distal and three proximal, in vitro binding sites for the glucocorticoid hormone-receptor complexes have been identified. We have prepared a series of 5' and 3' deletions of this region, using the exonuclease ExoIII. Combination of suitable 5' and 3' fragments enabled us to reconstitute the entire long terminal repeat with small internal deletions. The mutated long terminal repeats linked to the coding region of the Herpes simplex virus thymidine kinase gene were introduced into LTK- aprt- cells by transfection. Transcription from the mouse mammary tumor virus promoter in the presence or absence of hormone was assayed by nuclease S1 mapping. Deletion of the proximal in vitro binding sites resulted in a decrease in hormonal inducibility. When a synthetic oligonucleotide harboring the sequence of the distal in vitro binding site was inserted at the site of the proximal ones, hormone response was restored. This indicated that the distal binding site can replace the proximal ones in their hormone-regulatory function. However, insertion at the same site of an oligonucleotide containing the sequence 5' TGTTCT 3' found in all four binding sites, did not restore the hormone response, indicating that sequences flanking the TGTTCT motif are required for hormone response. Insertion of an unrelated DNA fragment at the site of the proximal binding element deletion completely abolished the hormone response. Analyses of different proximal binding-site deletion and insertion mutants suggested the presence of a transcriptional element located downstream from the most proximal hormone-receptor binding site.
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PMID:Functional analysis of the glucocorticoid regulatory elements present in the mouse mammary tumor virus long terminal repeat. A synthetic distal binding site can replace the proximal binding domain. 302 40

In the proviral DNA of mouse mammary tumor virus (MMTV), sequences up to approximately equal to 200 base-pairs from the RNA start site are required for stimulation of transcription by glucocorticoid hormones in cultured cells. A total of 26 mutant plasmids with clustered point mutations or small deletions in the hormone control region of the MMTV long terminal repeat were constructed, linked to the coding portion of the Herpes simplex virus thymidine kinase gene, and introduced by transfection into LTK- cells. Transcription from mutant DNA in the presence or absence of hormone was quantified by S1 nuclease protection assays. Our analysis revealed the presence of at least three control elements that affect the extent of transcription stimulation by glucocorticoid hormones: (1) a distal element, between -181 and -172 base-pairs from the RNA initiation site. Linker scanning mutants in this segment have a reduction of up to 20-fold in the hormone response with respect to wild type. (2) An element around position -120, defined by a mutation of 4 base-pairs between -121 and -117, which causes a fivefold reduction. (3) An element from approximately equal to -78 to -70, defined by a mutant with also a roughly fivefold lower stimulation. The first two are included in areas that have been shown by others to interact in vitro with hormone-receptor complexes; the last one overlaps the in vitro binding site of a nuclear protein factor. A mutant lacking all three elements (-193 to -70) is completely non-inducible by glucocorticoids. Together with earlier results obtained with 5' deletion mutants, the data show that the largest contribution to the stimulatory response is made by the distal element, which however does require the presence of both more-proximal ones for the response to be maximal. In the absence of the distal one, the two proximal elements together produce a residual stimulation in the order of 5 to 10% of wild type, while the -70 element alone is ineffective. In addition, we show that a functional TATA homology is required for maximum stimulation. It appears that transcriptional regulation of MMTV by glucocorticoid hormones is achieved by the concerted action of multiple sequence modules, not all of which correspond to receptor binding sites in vitro.
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PMID:Distinct sequence elements involved in the glucocorticoid regulation of the mouse mammary tumor virus promoter identified by linker scanning mutagenesis. 302 41